Fix condition for inclusion of math-finite.h for long double

The condition for declaration of long double functions in
math-finite.h was #ifdef __MATH_DECLARE_LDOUBLE before the
macroization of this file.  After the macroization, it was incorreclty
changed to #if __MATH_DECLARE_LDOUBLE, which broke the build for arm.

	* math/math.h: Fix check for __MATH_DECLARE_LDOUBLE.
	* math/bits/math-finite.h: Likewise.